Mix, who was listed at 6' 5" and 270 pounds, was an early proponent of weightlifting to enhance athletic power. He was years ahead of the curve that soon saw lineman and other football players taking up that practice to become better athletes. His lifts included a military press of 300 pounds, a clean and jerk of 325 pounds, and a bench press of 425 pounds, all of the lifts considered to be exceptionally strong for that era of play.

Mix attended the University of Southern California (USC) on a football scholarship.[4] There in 1959 he was a First Team All American, AP First Team All-Pacific Coast, First Team All Big Five, and won the USC Lineman Award.[4] He was a member of the Delta Chi Fraternity. At USC he minored in English, during his career Mix wrote a number of articles for Sports Illustrated.[5] He was elected the National Jewish College Athlete of the Year.[6]

He was a factor in the Chargers' early domination of the AFL's Western Division, and in San Diego helped them win an American Football League Championship in 1963, when they defeated the Boston Patriots 51-10 in the championship game. Mix was called for a mere two holding penalties in ten years.[1][9]

Mix was the first white player in the 1965 AFL All-Star game in New Orleans to step forward and join his black teammates in a civil rights boycott. The racist environment of New Orleans caused the black players to say they weren’t playing in a city that denied them the most basic rights (to eat, to get a cab, etc.). He made it clear that if the black players were not going to play, neither would he. That caused other white players to join the boycott. The game was then moved to Houston.[10]

He told the Chargers he wanted play again, but they had found a replacement in Gene Ferguson. After Mix asked to be traded to the New York Jets, San Diego traded him to the Oakland Raiders for two high draft picks in 1970 and 1971.[14] The deal was contingent upon Mix unretiring and agreeing to play for Oakland.[16] He played with the Raiders in 1971.[17] Then-Chargers owner Eugene V. Klein, who hated the Raiders, unretired Mix's number.[18]

In 2016, the IRS accused Mix of filing a false tax return. Federal prosecutors said that Mix got referrals for clients from a non-lawyer, a former professional basketball player client of his named Kermit Washington and that Mix made contributions to two charitable foundations of Washington that supported a school and other causes in Africa and then Mix took tax deductions for the contributions. Court records alleged that Washington diverted most of money donated to his charities for his own personal use. Mix pled guilty to one count of filing a false tax return. The plea agreement specifically said that Mix believed the charity was legitimate and did not know the funds were being diverted. Nonetheless, claiming the charitable contributions was wrong because Mix got something of value—the referrals.[22] US District Judge Greg Kays imposed a time-served sentence (less than probation).